1. Field of the Invention
The present general inventive concept relates to a method and an apparatus to synchronize an audio signal and a video signal, and more particularly, to a method and an apparatus to synchronize an audio signal and a video signal in multimedia.
2. Description of the Related Art
Since common multimedia, such as VCDs and DVDs, and common multimedia file formats, such as AVI, store audio and video synchronization information, an audio stream and a video stream are synchronized after decoding. However, even though an audio signal and a video signal decoded to suit a TV or a storage medium are synchronized, a user still experiences audio/video timing difference errors and lip synchronization errors since various delays in the audio signal and the video signal can cause significant lip synchronization problems.
Processing operations performed on the audio and video signals after the audio and video signals have been decoded and synchronized (i.e., post processing) can cause the various delays. The post processing includes audio signal amplification, an actual display procedure, and other factors. The delays added in audio and video signal paths may cause the audio signal and the video signal to be unsynchronized.
FIG. 1A is a block diagram illustrating a first conventional audio and video synchronizing apparatus. Referring to FIG. 1, a decoded audio signal is delayed by an audio delay unit 102 for a first predetermined time. An information format or mark of the delayed audio signal is changed by an audio post processing unit 104 before the audio signal is finally output. The changed audio signal is amplified by an amplifier 106 and reproduced by a speaker 108.
A decoded video signal is delayed by a video delay unit 112 for a second predetermined time. An information format or mark of the delayed video signal is changed by a video post processing unit 114 before the video signal is finally output. The changed video is displayed by a display unit 118.
A user manually inputs audio signal delay parameters according to the audio signal reproduced by the speaker 108 and the video signal reproduced by the display unit 118. The audio signal is matched to the video signal by a delay time of the audio delay unit 102 controlled according to the input audio signal delay parameters input by the user. Accordingly, the audio signal and the video signal may be resynchronized.
Alternatively with respect to the first conventional audio and video synchronizing apparatus, the user manually inputs video signal delay parameters. The video signal is then matched to the audio signal by a delay time of the video delay unit 112 controlled according to the input video signal delay parameters.
FIG. 1B is a block diagram illustrating a second conventional audio and video synchronizing apparatus. The second conventional audio and video synchronizing apparatus includes some of the same elements as the first conventional audio and video synchronizing apparatus of FIG. 1. Referring to FIG. 1B, the second conventional audio and video synchronizing apparatus performs a separate measuring operation to measure characteristics of audio and video signals using external sensors. In the measuring operation, a switch 152 is connected to a contact point ‘a,’ and an audio video synchronization unit 154 outputs synchronized audio and video test signals. The audio test signal is output from the speaker 108 after passing through the audio delay unit 102, the audio post processing unit 104, and the amplifier 106. The video test signal is displayed by the display unit 118 after passing through the video delay unit 112 and the video post processing unit 114.
The audio test signal output from the speaker 108 is received by a microphone 156, and the video test signal displayed by the display unit 118 is sensed by a light sensor 158.
The audio video synchronization unit 154 measures a time difference between a time when the audio test signal is received by the microphone 156 and a time when the video test signal is sensed by the light sensor 158. The measured time difference indicates a delay time of the audio test signal with respect to the video test signal, and vice versa.
The audio video synchronization unit 154 synchronizes the audio test signal and the video test signal by controlling a variable delay time of the audio delay unit 102 or the video delay unit 112 according to the measured delay time of the audio test signal with respect to the video test signal.
When the measuring operation is complete, decoded audio/video signals are reproduced by switching the switch 152 to a contact point ‘b.’
However, the first conventional audio and video synchronizing apparatus has a disadvantage in that a user is required to manually input audio signal delay parameters in order to resynchronize the audio signal and the video signal.
Additionally, the second conventional audio and video synchronizing apparatus has a disadvantage in that a separate measuring operation is required. Therefore, the separate measuring operation must be performed every time an audio or video signal path is changed (i.e., whenever a post processing operation is performed on either the audio signal or the video signal).